Therapeutic targeting of angiogenesis has become a novel approach to cancer therapy. The recent discovery of specific molecular targets that modulate the endothelial cell response and the development of suitable methods for assessing the contribution of these targets have given further impetus for the development and therapeutic application of an angiogenesis-targeted therapy. The small GTPase Rho and the major downstream effector, Rho kinase, is well established to regulate cell migration by the formation of stress fibers and the turnover of focal adhesions and plays a pivotal role in endothelial cell organization in angiogenesis. Several approaches have been developed to analyze the contribution of Rho kinase so far, and this chapter describes the in vitro and in vivo protocols used routinely in our laboratory to analyze the contribution in angiogenesis and shows the possibility of Rho kinase inhibitors in the clinical setting.